Recently, in consideration of environmental issues, vehicles using electric motors as driving power sources such as electric vehicles, hybrid vehicles and fuel cell electric vehicles have been attracting attention. Such a vehicle is provided with a rechargeable electric storage unit for supplying electric power to an electric motor and for converting kinetic energy to electric energy at the time of regenerative braking and for storing the same.
Use of an electric vehicle with such an electric storage unit as an electric power source of a house or the like has been proposed. By way of example, Japanese Patent Laying-Open No. 2001-008380 discloses a power management system that allows transmission of electric power between a house and a battery mounted on an electric vehicle.
Electric vehicles such as represented by hybrid vehicles are rapidly becoming common due in part to lower costs enabled by technical innovation. Along with the widespread use of electric vehicles, it is fully expected that a large number of households own a plurality of electric vehicles.
Japanese Patent Laying-Open No. 2000-209707 discloses a charging plan equipment for electric vehicles for leveling electric power usage and for realizing low running cost, when a plurality of electric vehicles are charged. The charging plan equipment forms a charging plan that makes power load for charging an object closer to desired power load conditions.
Among the electric vehicles mentioned above, hybrid vehicles that are most widely commercialized are capable of generating electric power, by receiving driving force from an internal combustion engine, such as an engine. Therefore, when a plurality of hybrid vehicles are electrically connected to each other, it is possible for each hybrid vehicle to receive electric power generated by any of the hybrid vehicles including itself and to charge the electric storage unit of itself.
Generally, fuel consumption efficiency of an internal combustion engine is known to vary dependent on rotational speed, generated torque and the like. Therefore, even when the same amount of electric power is generated, amount of fuel consumed for generating the electric power may differ in accordance with characteristics of each internal combustion engine.
The charge plan equipment disclosed in Japanese Patent Laying-Open No. 2000-209707 referred to above is devised for electric vehicles not including any internal combustion engine, and fuel consumption efficiency of the internal combustion engine has not been considered.